This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. This study seeks to establish the metabolic cost to an excitable cell associated with neurotransmitter-induced depolarization. Measurements of oxygen consumption from single cells were made using a modulation electrochemical technique. The cell chosen for these studies was the retinal horizontal cell, an important player in the processing of visual signals in the outer retina. Enzymatically isolated cells have a resting potential of approximately -70mV and depolarize in response to the excitatory neurotransmitter glutamate and its analogue, kainate. The depolarization induced by these agents mimics the tonic depolarization of horizontal cells normally observed in the intact retina under dark-adapted conditions. Our technique allows a direct comparison between the metabolic state measured at rest and following tonic depolarization. We found that the average resting O2 consumption for horizontal cells was 0.024 [unreadable]mol.cm-2.sec-1. Application of FCCP (10[unreadable]M), an uncoupler of oxidative phosphorylation, elevated oxygen consumption to 0.035 [unreadable]mol.cm2.sec-1;this elevation was followed by a sharp decline to below basal levels after 10min. 100[unreadable]M kainate elevated oxygen consumption from a basal average of 0.03 [unreadable]mol.cm-2.sec-1 to 0.07[unreadable]mol.cm-2.sec-1. Further, we were able to follow changes in O2 consumption in response to voltage clamp at 0 and -70mV. This data is one of the few examples where the metabolic cost of information processing has been measured from a single identifiable cell. The development of this approach has great promise for furthering our understanding of neuronal metabolism, degenerative diseases and aging.